CuBr2-mediated direct aqueous bromolactonization of 2,3-allenoates. An efficient access to β-bromobutenolides

An efficient procedure for the synthesis of β-bromobutenolides was developed. 2,3-Allenoates with different substitution patterns react with CuBr2 in aqueous ethanol at 80–85°C to afford the corresponding β-bromobutenolides in moderate to excellent yields (up to 97%).